Mass selector does not perform indefinite zoom

prasopes/__main__.py

@@ -57,9 +57,9 @@ def main():
     gt.zoom_factory(spectrum, 1.15, ms)
     mass_selector = SpanSelector(
         spectrum, lambda x_min, x_max: gt.pick_masses(
-            x_min, x_max, spectrum, ms),
-        'horizontal', useblit=True, rectprops=dict(
-            alpha=0.15, facecolor='purple'), button=3)
+            x_min, x_max, spectrum, ms), 'horizontal', minspan=0.01,
+        useblit=True, rectprops=dict(alpha=0.15, facecolor='purple'),
+        button=3)
     time_selector = SpanSelector(
          chromatogram, lambda x_min, x_max: gt.pick_times(
              x_min, x_max, spectrum, ds, chromatogram, ms, chrom),